1. Field of the Invention
The present invention generally relates to a reverse rotation control apparatus for a two-cycle engine which makes it possible to drive a motor vehicle equipped with the two-cycle engine in a rearward direction by reversing rotation of the engine. More specifically, the present invention is concerned with a reverse rotation control apparatus for a two-cycle engine of a motor vehicle which apparatus can realize a reverse rotation control with inexpensive structure.
2. Description of Related Art
In general, a four-cycle engine mounted on a motor vehicle such as a passenger car or the like is equipped with a clutch and a gear box at an output side of the engine for deriving the output power thereof by way of the clutch and the gear box.
However, in the case of small-size motor vehicles for specific purposes such as snowmobiles, all-terrain vehicles and the like, a two-cycle engine of low cost is mounted. In this conjunction, it is further noted that in the case of these motor vehicles, the space for installing the engine is limited.
Such being the circumstances, no gear box is ordinarily installed as the reverse rotation control apparatus for the two-cycle engine in the motor vehicles of the types mentioned just above, wherein the output torque of the engine is derived by way of a centrifugal-type automatic transmission constituted by a V-belt transmission.
Consequently, the motor vehicle can not be driven in other direction than the forward direction. Thus, manpower is required for moving the motor vehicle rearwards as is in the case where the motor vehicle is to be taken out from a garage or it is to be disburden from a lorry, giving rise to a problem that the motor vehicle is very inconvenient to handle.
Under the circumstances described above, it has been proposed that a clutch and a gear box are provided equally for the motor vehicle equipped with the two-cycle engine by affording a sufficient space for installation of the two-cycle engine so that the traveling directions (forward and rearward directions) of the motor vehicle can be changed over by manipulating a gear change lever, as in the case of the four-cycle engine.
For having a better understanding of the concept underlying the present invention, a hitherto-known or conventional reverse rotation control apparatus for a two-cycle engine of a motor vehicle will be reviewed in some detail.
FIG. 4 is a block diagram showing schematically and generally a configuration of a two-cycle engine system equipped with a prior art reverse rotation control apparatus for a motor vehicle in which a conventional gear box is employed.
Referring to FIG. 4, an internal combustion engine (hereinafter referred to simply as the engine) 1 driven in two cycles (i.e., two-cycle engine) is installed on a motor vehicle (not shown). The engine 1 has an output shaft 2 which rotates in one direction as indicated by an arrow, wherein a driving torque generated by the engine 1 is outputted through the medium of a clutch 3 and a gear box 4. Parenthetically, the gear box 4 is provided with a back gear train for allowing the motor vehicle to be driven backwardly or rearwardly.
Furthermore, a change lever 5 is provided in the gear box 4 for allowing a driver to manually change over gear trains. A rotation sensor 6 for detecting the engine speed (rpm) as well as angular position of a crank shaft (or crank angle, to say in another way) of the engine is implemented in the form of an electromagnetic pickup device or the like and provided in association with the output shaft of the engine 1. A rotation signal SG derived from the output of the rotation sensor 6 is inputted to an ignition control unit 10 which may be constituted by a microprocessor or microcomputer.
The ignition control unit 10 is so designed or programmed as to arithmetically determine control timings for the engine 1 for issuing an ignition signal P on the basis of operating state information which includes not only the rotation signal SG mentioned above but also other signals derived from the outputs of other various sensors (not shown).
Further provided is an ignition coil 11 which is realized in the form of a transformer having a primary winding and a secondary winding for generating in response to the ignition signal P a secondary voltage boosted up upon interruption of the primary current, whereby a high voltage for firing is applied to a spark plug 12 of the engine 1. In this conjunction, it is to be noted that the engine 1 undergoes rotation control in a predetermined direction by controlling the ignition timing on the basis of the rotation signal SG.
In the two-cycle engine of a motor vehicle equipped with the conventional reverse rotation control apparatus such as shown in FIG. 4, the rotation output or output torque of the engine 1 can be lowered as desired through the medium of the gear box 4 while the driving direction of the motor vehicle can be changed over between the forward direction and the rearward direction with the aid of the back gear train.
However, with the arrangement shown in FIG. 4, difficulty will be encountered in securing a space around the engine 1 for affording accommodation and installation of the gear box 4. In particular, in the case of the snowmobile and the all-terrain vehicle mentioned previously, difficulty is encountered in making available an engine room for accommodating therein the engine 1 itself. Consequently, additional provision of the gear box 4 will incur remarkable increase in the manufacturing cost of these types of motor vehicles.
At this juncture, it is noted that the two-cycle engine has a feature that the crank shaft can be rotated in either in the forward or reverse direction as desired by controlling the ignition timing, differing from the four-cycle engine.
In actuality, there has been proposed a reverse rotation control apparatus for a two-cycle engine in which the feature mentioned above is made use of. By way of example, there is disclosed in U.S. Pat. No. 5,036,802 issued in 1997 such a reverse rotation control apparatus for a two-cycle engine of a motor vehicle which makes it possible to drive the motor vehicle either in the forward direction or in the rearward direction through the reverse rotation control of the engine 1 by using a centrifugal-type automatic transmission (not shown) without resorting to the use of the gear box 4.
In the case of the reverse rotation control apparatus disclosed in the U.S. Patent specification cited just above, when a driving direction of a motor vehicle equipped with a two-cycle engine is to be reversed, a driver manipulates a rotation reversing lever when the engine 1 is in a normal rotation state (corresponding to e.g. forward traveling of the motor vehicle). Then, the ignition control unit 10 lowers the rotation speed (rpm) of the engine 1 by forcibly causing misfire to take place in the engine 1. When the engine rotation speed has thus been lowered to a predetermined rotation speed (e.g. 500 rpm) which is suited for the reverse rotation control (i.e., control for reversing the rotating direction of the engine), the ignition timing at which the ignition signal P is applied is caused to advance excessively or overadvance beyond an ordinary advanced control position (which lies ordinarily within a range of 5.degree. to 30.degree. before the top dead center TDC in terms of crank angle (i.e., range of BTDC 5.degree. to 30.degree.). With the overadvance control of the ignition timing mentioned above, the ignition timing is set, for example, at BTDC 40.degree. (i.e., at a crank angle of 40.degree. before the top dead center), for thereby allowing the engine 1 to transit from the normal rotation state (corresponding to e.g. forward running of the motor vehicle) to the reverse rotation state (corresponding to e.g. rearward driving of the motor vehicle).
Thereafter, the ignition control unit 10 regards the reverse rotation direction as the normal rotation direction and the ignition signal P is generated at the ordinary ignition timing for sustaining continuously the reverse rotation state of the engine 1. Thus, the motor vehicle can be driven backwardly or in the reverse direction. Parenthetically, when the engine 1 is to be restored from the reverse rotation state to the normal rotation state, the control process similar to that described above is carried out by regarding the current rotating direction of the engine (i.e., the reverse rotation) as the normal rotating direction.
However, with the reverse rotation control apparatus described above, it is necessary to detect that the engine rotation number or engine speed (rpm) has been really lowered to a predetermined rotation number. To this end, it is required to monitor constantly the rotation number of the engine 1 for comparing it with a predetermined rotation number, which will increase not only the cost but also the load imposed on the ignition control unit 10, giving rise to a problem.
As is apparent from the foregoing, the reverse rotation control apparatus for the two-cycle engine for a motor vehicle suffers a problem that when the gear box 4 such as shown in FIG. 4 is employed, there arises the necessity for ensuring a space for installation of the gear box 4 around the engine 1, which will of course lead to increasing of the manufacturing cost of the engine and hence the motor vehicle.
On the other hand, in the reverse rotation control system for the engine 1 in which the engine rotation number is once lowered and then the ignition timing is overadvanced, as is disclosed in U.S. Pat. No. 5,036,802, there arises the necessity for monitoring the engine rotation speed (rpm) up to a time point immediately before the start of the overadvanced ignition timing control in order to decide that the engine rotation speed has decreased to the predetermined level suited for the rotation reversing control, increasing ultimately not only the cost of the engine system but also the burden imposed on the ignition control unit 10, giving rise to another problem.